Noble metal alloys adapted for ceramic bonding (the application of a porcelain jacket or covering) are well known in dentistry and are used in the manufacturing of crowns, bridges, and other prosthetic appliances. These so called noble "ceramic alloys" typically consist of 80-90% gold, 5-15% platinum and 1-10% palladium. The newer alloys consist of 51.5% gold, 8.5% indium, 1.5% gallium, and 38.5% palladium. Alloys of this type and application of such alloys in dentistry are discussed in detail in U.S. Pat. No. 3,413,723, Wagner and Pralow and in U.S. Pat. No. 4,123,262, Cascone. For brevity, the disclosures of these patents are incorporated herein by reference.
Due to the increase in price of gold and platinum, lower cost palladium alloys were developed. U.S. Pat. No. 3,929,474, discloses a palladium-silver system. U.S. Pat. No. 3,819,366, discloses a palladium-indium-silver or palladium-indium-silver-gold system. Palladium alloys contain silver which causes discoloration in porcelain as described by R. V. Williams, Jr., et al in Dental Porcelain: The State of the Art1977, Henry N. Yamada, editor, 1977, University of Southern California School of Dentistry, Los Angeles, CA, pages 71-77. U.S. Pat. No. 3,928,913 discloses a palladium-cobalt alloy for ceramic bonding. It is difficult to match the shades of the porcelain due to the formation of blue oxide during the firing process.
Coloration of porcelain may be limited by baking one layer of gold powder onto the understructure of the alloy prior to the application of dental porcelain. However, this technique increases cost (gold powder and labor), and causes uncertainty of porcelain/metal bond strength. The introduction of certain elements described in U.S. Pat. No. 4,194,907, overcomes the discoloration problem with respect to certain alloys. Another way to avoid this problem is the elimination of the use of silver or cobalt as described by Prosen in U.S. Pat. No. 4,046,561, U.S. Pat. No. 4,124,382, and U.S. Pat. No. 4,179,288. Prosen continuously works to improve the ductility of the alloy which is an important characteristic of dental alloys especially when margins of the crown needed to be burnished.
The object of this invention is to develop a palladium alloy which forms a light shade of oxide during the firing of porcelain. The oxide does not discolor the porcelain. Another object of this invention is to develop a palladium alloy which remains ductile even after the firing processes of porcelain.